1. Field of the Invention
This invention relates to methods of removing unwanted impurities from water. In particular this invention relates to methods of removing unwanted hydrocarbons, especially low molecular weight monocyclic aromatic hydrocarbons, from water.
2. State of the Art
Oilfield-produced waters, remediation site waters, and refinery runoff streams all contain high concentrations of hydrocarbons. These petroleum processing derived waste waters contain particularly high concentrations of several classes of organic compounds due to the high water solubility of these classes of compounds. The low molecular weight monocyclic aromatic hydrocarbons, and some other structurally related non-hydrocarbon monocyclic aromatic compounds, for example, benzene, toluene, ethylbenzene, and the three isomers of xylene, styrene, and pyridine (a mixture of at least three of the above named components will hereinafter referred to as BTEX), comprise one such class of relatively highly water soluble hydrocarbons. However, other less soluble hydrocarbons, such as aliphatic hydrocarbons found in diesel and jet fuels and in gasoline, also pollute water and must be removed. Because of health concerns, regulators reduced the maximum acceptable concentration of BTEX in water to below 5 ppmw. Consequently, producers of BTEX contaminated water need to remove or greatly reduce the concentrations of all these polluting hydrocarbons in produced aqueous runoff streams.
Several technologies allow treatment of water to reduce the concentrations of BTEX and other hydrocarbons. These technologies include UV/ozone oxidation, UV/peroxide oxidation, high intensity UV destruction, powdered activated carbon adsorption coupled with biological treatment, granular activated carbon adsorption, air/gas stripping followed by carbon adsorption, various membrane processes, and supercritical water oxidation. While all of these technologies work acceptably well, they all require a fairly large physical plant to treat water produced on an industrial scale. For that reason, space-critical producers, for example, off shore oil platforms and the like, require different techniques to process the water they produce. A need exists for an effective water remediation method easily usable in space-critical areas.
Countercurrent technology presents a candidate for a small, space-critical water remediation unit since countercurrent installations typically have a small "footprint", that is, they are installations that require little plant area. Conventionally, countercurrent units soften and deionize water. In these conventional units, a countercurrent ion exchange resin removes inorganic components, for example, cations such as magnesium, iron or calcium, or inorganic anions. However, no countercurrent adsorption method has been designed to remove organic components, such as BTEX, diesel and gasoline components.
It would be advantageous to have a small footprint countercurrent unit that removes BTEX and other hydrocarbons from water to a maximum concentration of less than 5 ppmw. The inventor has found that countercurrent technology can provide a unit that removes at least 75% of the total BTEX from a waste water stream. The unit also provides a means to remove other, non-aromatic hydrocarbons from a waste water stream.